In recent years, hyperlipemia and arteriosclerosis derived therefrom have been rapidly increased with the change to western eating habits with high-calory and high-cholesterol foods bused on the higher level of life and with the advance of age of the population, and this has been one of social problems. The conventional pharmacotherapy of hyperlipemia and arteriosclerosis has mainly put stress on the decrease in blood lipid that causes these diseases, and the lesion of the arteriosclerosis itself has not been treated as a target. Acyl coenzyme A cholesterol acyltransferase (ACAT) is an enzyme that catalyzes synthesis from cholesterol to cholesterol ester, and plays a vital role in metabolism of cholesterol and absorption thereof in digestive organs. Inhibition of the ACAT enzyme that catalyzes esterification of free cholesterol in epithelial cells of the small intestine results in inhibition of absorption of cholesterol from the intestine, and inhibition of synthesis of cholesterol ester in the liver based on the ACAT inhibition results in suppression of secretion of VLDL from the liver to the blood. These results are considered to lead to an activity of decreasing blood cholesterol. Most of conventional ACAT inhibitors have been expected to exhibit an activity of decreasing blood cholesterol as an antihyperlipemic agent by acting on the ACAT enzymes in the small intestine and the liver.
For example, as an ACAT inhibitor, the specification of U.S. Pat. No. 4,716,175 describes 2,2-dimethyl-N-(2,4,6-trimethoxyphenyl)dodecanamide, and European Patent No. 372,445 describes N′-(2,4-difluorophenyl)-N-[5-(4,5-diphenyl-1H-imidazol-2-ylthio)pentyl]-N-heptylurea. However, most of the conventional ACAT inhibitors have put stress on an activity of decreasing blood cholesterol as an antihyperlipemic agent, and the administration thereof at a high dose for exhibiting its activity has often caused side effects such as intestinal bleeding, intestinal disorders, diarrhea, hepatopathy and the like at the stage of a clinical test, making difficult the clinical development thereof.
The arteriosclerosis is inherently a characteristic lesion such as intima hypertrophy and lipidosis of the blood vessel. According to the recent studies, suppression of foamation of macrophages that play a main role in formation of the arteriosclerosis lesion has been expected to lead to regression of the arteriosclerosis lesion itself. Foam cells derived from macrophages (cholesterol ester is stored in cells as fat droplets) have been observed in the gruel arteriosclerosis lesion, and the foamation of macrophages is deemed to deeply participate in the progression of the lesion. Further, it has been reported that the ACAT activity in the blood vessel wall in the arteriosclerosis lesion site is increased and cholesterol ester is stored in the blood vessel wall (refer to Gillease, J. et al., Exp. Mole. Pathol., 44, 329-339 (1986)).
The inhibition of esterification of cholesterol with an ACAT inhibitor results in formation of free cholesterol in cells, and this free cholesterol is removed with high-density lipoprotein (HDL), transferred to the liver (inversely transferred with HDL), and metabolized. Accordingly, suppression of storage of cholesterol ester in the lesion site is expected. As a result, it is considered to provide a direct anti-arteriosclerotic activity. There is a report that ACAT includes two types, a type present in the small intestine and a type present in the blood vessel wall [Kinunen M. et al., Biochemistry, 27, 7344-7350 (1988)]. However, many of the past researches on the ACAT inhibitor have been conducted using an enzyme of a type present in the small intestine and the liver [Tomoda Elichi et al., J. Antibiotics, 47, 148-153 (1994)].
The present inventors considered that medications which selectively inhibit an ACAT enzyme of a type present in the blood vessel wall can be those for treating arteriosclerosis that give less side effects, and have conducted synthesis and researches of such inhibitors.
The present inventors continued studies for achieving this object, and found in advance that compounds represented by the formula (IV)                 wherein         represents an optionally substituted divalent residue such as benzene, pyridine, cyclohexane or naphthalene or a group,         Ar represents an optionally substituted aryl group        X represents —NH—, an oxygen atom or a sulfur atom,        Y represents —NR4—, an oxygen atom, a sulfur atom, a sulfoxide or a sulfone,        Z represents a single bond or —NR5—,        R4 represents a hydrogen atom, a lower alkyl group, an aryl group or an optionally substituted silyl lower alkyl group,        R5 represents a hydrogen atom a lower alkyl group, an aryl group or an optionally substituted silyl lower alkyl group, and        n is an integer of from 0 to 15,or salts or solvates thereof, and compounds represented by the formula (V)         wherein         represents an optionally substituted divalent residue such as benzene, pyridine, cyclohexane or naphthalene, or a group,         Ar represents an optionally substituted aryl group,        X represents —NH—, an oxygen atom or a sulfur atom,        Y represents —NR4—, an oxygen atom, a sulfur atom, a sulfoxide or a sulfone,        Z represents a single bond or —NR5—,        R4 represents a hydrogen atom, a lower alkyl group, an aryl group or an optionally substituted silyl lower alkyl group,        R5 represents a hydrogen atom, a lower alkyl group, an aryl group or an optionally substituted silyl lower alkyl group,        l is an integer of from 0 to 15,        m is an integer of 2 or 3, and        n is integer of from 0 to 3,or salts or solvates thereof have an excellent ACAT inhibitory activity, and they applied the same for patents (Japanese Patent Application Nos. 88,660/1997, 90,146/1997 and 149,892/1997).        
Further, as compounds similar to the compounds represented by the formula (I), 3-(benzothiazol-2-ylthio)-N-(phenyl)propanamide is disclosed in J. Chem. Eng. Data, 27, 207 (1982), and 3-(benzoxazol-2-ylthio)-N-(phenyl)propanamide in Fungitsidy, Ed. Melnikov, N. N. Izd. Fan Uzb. SSR: Tashkent, USSR. 82-88 (1980). However, these compounds are not only those in which an amide moiety is a phenyl group, but also these documents are totally devoid of the description that the compounds have an ACAT inhibitory activity.
Thus, the present inventors found that the compounds represented by the formula (IV) or (V) have an organ-selective ACAT inhibitory activity and an intracellular cholesterol transfer inhibitory activity, and that these are useful as an antihyperlipemic agent having an activity of decreasing blood cholesterol and as an agent for preventing and treating arteriosclerosis having a macrophage foamation inhibitory activity.
However, the compounds represented by these formulas (IV) and (V) did not necessarily have a sufficient activity, nor was the organ-selectivity satisfactory.
Under these circumstances, the present inventors have conducted further investigations to develop an ACAT inhibitor having a superior ACAT inhibitory activity, and have consequently found that the compounds represented by the formula (I) are useful ACAT inhibitors which conquer the above-mentioned defects. This finding has led to the completion of the present invention.